In the past there has been extensive description in the patent and other technical literature relating to electrophoretic migration imaging processes and colorants useful therein. For example, a description of such processes and colorants may be found in Sugarman, U.S. Pat. No. 2,758,939, issued Aug. 14, 1956; Kaprelian, U.S. Pat. Nos. 2,940,847; 3,100,426; 3,140,175; and 3,143,508; Tulagin et al., U.S. Pat. Nos. 3,384,565; 3,384,488; 3,615,558; Clark, U.S. Pat. No. 3,384,566; and Yeh, U.S. Pat. No. 3,383,993. In addition to the foregoing patent literature directed to conventional photoelectrophoretic migration imaging processes another type of electrophoretic migration imaging process which advantageously provides for image reversal is described in Groner, U.S. patent application Ser. No. 607,650, filed Aug. 25, 1975.
However, regardless of the particular electrophoretic migration imaging process employed, an essential component of any such process is the electrically photosensitive particles. And, of course, to obtain an easy-to-read, visible image it is important that these electrically photosensitive particles be colored as well as electrically photosensitive. Accordingly, as is apparent from the technical literature regarding electrophoretic migration imaging processes, work has been carried on in the past and is continuing to find colorants which possess useful levels of electrical photosensitivity and which exhibit good colorant properites. Thus, for example, various types of electrically photosensitive materials are disclosed for use in electrophoretic migration imaging processes, for example, in Sugarman, U.S. Pat. No. 2,758,939; Kaprelian U.S. Pat. No. 2,940,847; Tulagin et al., U.S. Pat. No. 3,384,488 and U.S. Pat. No. 3,615,558 noted hereinabove.
In large part, the art, to date, has generally selected useful electrically photosensitive or photoconductive pigment materials for electrophoretic migration imaging from known classes of photoconductive materials which may be employed in conventional photoconductive elements, e.g., photoconductive plates, drums, or webs used in electrophotographic office copier devices. For example, both Sugarman and Kaprelian in the above-referenced patents state that electrically photosensitive materials useful in electrophoretic migration imaging processes may be selected from known classes of photoconductive materials. And, the phthalocyanine pigments described as a useful electrically photosensitive material for electrophoretic imaging processes in Tulagin et al., U.S. Pat. No. 3,615,558 have long been known to exhibit useful photoconductive properties.
It is recognized, as set forth above, that many useful electrically photosensitive materials which are employed in electrophoretic migration imaging processes can be and have been selected from known photoconductive materials. However, in accord with the present invention, a class of electrically photosensitive materials has been discovered which is believed to represent a new class of materials. In this regard, it is noted that Johnson, U.S. Pat. No. 3,681,008 issued Aug. 1, 1972, describes certain julolyl group-containing organic photoconductors. However, although the julolyl group is common to the compounds of U.S. Pat. No. 3,681,068 and certain of the electrically photosensitive materials of the present invention, the overall molecular structure of the compounds of U.S. Pat. No. 3,681,068 and those of the present invention is quite different.
Another class of photoconductive materials somewhat similar to those described in the present application are the known organic photoconductive materials including, but not limited to, those materials described in U.S. Pat. Nos. 3,246,983 issued Apr. 19, 1966, 3,567,450 issued Mar. 2, 1971, 3,653,887 issued Apr. 4, 1972, and 3,873,312 issued Mar. 25, 1975. Certain materials within the aforementioned class of organic photoconductive materials have recently been found to possess electrical photosensitivity properties useful in electrophoretic migration imaging processes. These latter materials are described in our copending U.S. patent application Ser. No. 645,005, filed concurrently herewith and entitled Electrophoretic Migration Imaging Process, Case A. However, the molecular structure of the electrically photosenstive material used in the present invention is specifically different from that of the organic photoconductors described in the aforementioned patents and also is different from that of the electrically photosensitive material described in our copending patent application. Moreover, the electrically photosensitive material used in the present invention advantageously exhibits improved levels of electrical photosensitivity in comparison to the material described in our copending patent application.